As the number of electronic devices has recently been increased, the individual devices are mutually interfered with electromagnetic waves emitted from the devices, which increasing the risk of their malfunction. In addition, an electronic device may also malfunction due to an electromagnetic wave emitted from the device itself The effect of the electromagnetic wave emitted from the electronic device on a living body is also a matter of concern.
Therefore, an electromagnetic wave absorber for absorbing a harmful electromagnetic wave with high efficiency has increasingly been developed in recent years, and various shapes of the electromagnetic wave absorber and methods of manufacturing the same have been proposed.
For example, Japanese Patent Laying-Open No. 2000-353610 discloses a method of manufacturing an electromagnetic wave absorber including the steps of blending and kneading a finely-ground soft magnetic material and a thermoplastic binder to produce pellets of a given particle size, which are then heated and pressurized to be injected into a pair of molds having a space corresponding to an electromagnetic wave absorber to be manufactured to provide a compact, baking the compact at approximately 300-600° C. to thermally decompose the contained thermoplastic binder and degreasing the compact, and baking the degreased compact at approximately 1000-1350° C. to sinter the soft magnetic material and provide a sintered compact, in order that a thin-walled, three-dimensional electromagnetic wave absorber having a fairly constant permeability can be manufactured at low costs.
The electromagnetic wave absorbing performance of the electromagnetic wave absorber is mainly determined by its shape and material. Therefore, in the case of the three-dimensional shape as in the electromagnetic wave absorber described in Japanese Patent Laying-Open No. 2000-353610, an electromagnetic wave absorber having a larger height is thought to exhibit higher electromagnetic wave absorbing performance. However, it is difficult to manufacture an electromagnetic wave absorber having a larger height.
The document above does not describe how high an electromagnetic wave absorber is to be made so that the absorber can be manufactured with high yields while its electromagnetic wave absorbing performance is kept high. Therefore, it is difficult to obtain, with high yields, an electromagnetic wave absorber excellent in electromagnetic wave absorbing performance. Furthermore, the method described in the document above tends to cause quenching cracks after sintering, which contributes to the reduction in yield.
For an electromagnetic wave absorber used for an anechoic chamber and others, one made of urethane sponge impregnated with carbon is generally used. However, such an absorber has low strength and is highly flammable, resulting in poor durability. If such an absorber is used for a floor material, it is necessary to reinforce the absorber with another member. Disadvantageously, such an absorber also has a water-absorbing property, which lowers its electromagnetic wave absorbing performance, and has low weather resistance, which makes the same unusable outdoors and under the circumstances of high temperature and high humidity.